The present invention relates to a process for preparing a planographic printing plate for an ink-jet recording system, and especially, to a process for preparing a printing plate for a hot melt type ink-jet system which is satisfactory in image qualities of both the printing plate and printed matter.
On account of the recent progress in office appliances and office automation, an offset planographic printing system spreads throughout the small printing field, in which a printing plate is prepared, that is, image formation is performed by various processes on a fresh direct drawing type planographic printing plate precursor that has on a water-resistant support an image receiving layer having a water-receptive surface.
In conventional direct drawing type planographic printing plate materials, image accepting layers (or image receiving layers) containing inorganic pigments, water-soluble resins, and water resistance enhancers are provided on supports such as paper having undergone a water resistance treatment and plastic films. In known processes for making printing plates, lipophilic images are formed on such fresh direct drawing type planographic printing plate precursor by the use of lipophilic inks, with typewriters, by handwriting, by hot melt transfer of images from ink ribbons with heat transfer printers, or by the use of ink-jet printers using liquid inks.
The printing plates thus made, however, fail to have sufficient mechanical strength in the image areas which causes falling off of the image areas during printing.
In platemaking by the use of the ink-jet printers in which liquid inks are used, in order to prevent image forming agents in the liquid inks from diffusing or being absorbed in the plate materials and mitigate blurs of images, JP-A-64-27953 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a hot melt type ink-jet process (occasionally referred to as a xe2x80x9csolid-jet processxe2x80x9d) in which a hydrophobic solid ink that changes to a liquid by hot melting is used. The image receiving layer of a printing plate precursor used herein has a water receptive surface.
Even in this process, however, blurs are actually observed in image areas of printed matter obtained from the printing plate thus made, and in addition, the number of sheets which can be printed is inadequately only a few hundred at most.
An object of the present invention is to provide a process for preparing a printing plate of a hot melt type ink-jet system from which a number of printed sheets having sharp images can be obtained.
The object given above has been achieved by embodiments of the present invention as described in the following items (1) to (4):
(1) A process for preparing an ink-jet system printing plate, wherein an image is formed according to a hot melt type ink-jet system by heat-melting an ink composition that is solid at ordinary temperature, spraying droplets of the ink composition in a hot melt state from nozzles onto an intermediate transferrer to form an image, and contact-transferring the image on the intermediate transferrer to an image receiving layer of a planographic printing plate precursor, the image receiving layer being provided on a water-resistive support and containing zinc oxide and a binder resin, and thereafter, a nonimage area of said image receiving layer is desensitized by chemical reaction treatment to prepare a planographic printing plate.
(2) A process for preparing the ink-jet system printing plate as described in item (1), wherein the surface of the image receiving layer of the planographic printing plate precursor has a Bekk smoothness degree of at least 30 seconds per 10 ml and a water-contact angle of 50xc2x0 or more.
(3) A process for preparing the ink-jet system printing plate as described in item (1), wherein the ink composition contains a wax having a melting point of from 50xc2x0 to 150xc2x0 C., a resin, a color material, and an adhesion modifier and turns to a hot melted liquid by heating to 80xc2x0 C. or higher, the hot melted liquid having a viscosity of from 1 to 20 cps.
(4) A process for preparing the ink-jet system printing plate as described in item (1), wherein the support surface adjacent to the image receiving layer has a Bekk smoothness degree of at least 300 seconds per 10 ml.
In the present invention, a hydrophobic ink image is formed on the hydrophobic image receiving layer containing zinc oxide according to the hot melt type ink-jet system, and a nonimage area is then made water-receptive. Therefore, the system of the present invention provides much more improved images to both the printing plate precursor and printed matter, and in addition, an excellent press life to the printing plate, as compared with a hot melt type ink-jet system in which a hydrophobic ink image is formed on a water-receptive image receiving layer. Further, use of the intermediate transferrer enables pressure and temperature of ink to be appropriately controlled when transferred to a printing plate precursor, and holding power of an image to the printing plate precursor can also be extremely increased, which also makes it possible to improve the press life of the printing plate precursor.